Protease activated receptor-1 (PAR-1) is a G protein coupled receptor (GPCR) that is highly expressed on neurons and microglia. Levels of PAR-1 activators, including plasmin and matrix metalloproteinases (MMPs), are substantially increased in HIV associated neurological disorders (HAND) and one study has shown that levels of PAR-1 are increased as well. Though not yet studied in the context of HAND, PAR-1 antagonists can prevent microglial activation and neurotoxicity in animal models of Parkinson's disease and cerebral ischemia. Recent studies have shown that select GPCRs can associate with -arrestins to activate the kinase glycogen synthase kinase-3 (GSK-3) through a novel, non-canonical signaling pathway. Importantly, GSK- 3 inhibitors have been shown to reduce neuronal injury in response to HAND relevant stimuli. In addition, increased GSK-3 activity has been implicated in HAND relevant pathology including microglial activation, neurotoxicity, and long term depression of synaptic transmission. In the present dual PI R01 proposal, we hypothesize that excess activation of PAR-1 stimulates non- canonical GPCR dependent signaling pathways to measurably contribute to HAND relevant microglial activation and neuronal injury. Our plan will be to test underlying mechanisms with in vitro studies (Aims 1 and 2) and the relative in vivo importance of this pathway to phenotypic changes observed in mouse models (Aim 3). Preliminary data in support of our hypothesis will include evidence for GSK-3 activation and cognitive impairment in mice that overexpress a potent PAR-1 agonist. Preliminary data will also show evidence for PAR-1 dependent, non-canonical signaling, in CNS derived cells isolated from these animals. Innovation comes from the study of a relatively unexplored receptor as related to HAND, the study of a novel signaling pathway for this receptor, and the use of a unique mouse model. Innovation also comes from techniques that include recordings of neuronal activity via multielectrode arrays, and small animal magnetic resonance spectroscopy. The overall goal of our proposal is to identify targets for adjunct therapeutics. If PAR-1 activation can stimulate HAND relevant pathology through increased GSK-3 activity, novel drugs being developed to more specifically inhibit the activity of this kinase could be considered for treatment of this condition. Moreover, newly developed orally available PAR-1 antagonists that are now in clinical trials for coronary artery disease might be considered for treatment of the same.